Method of producing half-tone negatives.



W, 'R. B. LARSEN. METHOD OF PRODUCING HALF TONE NEGAT$VES.- APPLSCATION msn r1ov.14, 1911.

1,167,505., Patented Jan 11, 1916.

mm Weak, mwm.

Wu H ewes WERNER ROBERT mason Lassen, or cornnnaenn, DENMARK. 7

METHOD OF PRODUCING I HALF-TONE NEGATIVES.

Application filed November 14, 1911.

To all whom it may concern Be it known that I, WERNER .RoBERr Boson LARSEN, of Copenhagen, Denmark, have invented a new and useful Im rovement in Methods of Producing Hal -Tone Negatives, of which the following is a full, clear, and exact description- My invention relates to improvements in the method of producing autotypic halftone negatives of the kind in which the number and size of the printing elements in the lights are smaller than in the shadows. In the production of half-tone negatives, it is customary to use two screens, which are used successively, and which are constructed in such a manner that the last screen used has areas of opacity corresponding to the light openings in the first screen, but being lesser. in number than said openings. In carrying out this method, however, only one screen at a time is used between the sensitive plate and the lens, as when the first screen has been used, the same is removed and replaced by the second, and the latter has to be adjusted in sucha manner that its opaque elements coincide exactly with the places where the opaque elements of the first used screen were situated during the first part of the exposure, and it is very diiiicult to eifect this adjustment, especially when fine screens are used. It will also be noted that a good result depends absolutely upon the accuracy with which the adjustment of the last fected. 1

The object of my invention is to obviate the above diiiiculty, and provide for the simultaneous use of, two screens between the sensitive plate and the lens, and to construct the screens and have their opaque elements so arranged that according to the design to be printed, they may both remain in an unaltered position during the Whole exposure, only one exposure being used, or they may be used together in front of the sensitive plate during a part of the exposure, and the front screen removed during the latter part, all this depending upon the nature of the design to be printed.

In carrying out my improved method, an ordinary line screen is most conveniently used as a front screen, while the rear screen is a dot screen, the opaque elements of which are arranged behind the intersections of the lines in the front screen, and are Specification of Letters Patent.

screen has been efhave exactly double the Patented Ja n. 11, 1916.

Serial No. 680,289.

fewer in number than the points of intersection in said line screen.

Reference is to be had to the accompanying drawings forming a part of this specification, in which similar reference characters indicate corresponding parts in all the views.

Figure 1 is a broken front view of an ordinary line screen. Figs. 2 and 3 show fragments of the dot screen but with the opaque elements of different-shape. Figs. 4 and 5 are fragments of the dot screen showing still other variations of the opaque elements, and Figs. 6 and 7 are diagrammatic views showing the manner in which the exposure is effected and the printing done on the sensitive plate.

In Fig. 1 the line screen 10 has the usual intersecting lines It, and in Fig. 2 the screen 11 is provided with dots a which when the screen 11 is placed behind the screen 10, can be made to coincide with certain points of intersection of the lines It. In Fig. 3 the plate 11 shows opaque elements or dots b, and while the screen is used in the manner above described, the elements are-of different shape so as to produce a diflerent design. As shown in Figs. 2 and 3, the opaque elements a and b are one-quarter in number of the number of points of intersection of the lines it on the screen 10. Also for the purpose below described, the screens shown in Figs. 2 and 3 have a pitch difiei'ing somewhat from the double of the pitch of the line screen, whereas the screen shown in Figs. 4 and 5 with the elements a and of, pitch of the line screen. This is because the screens shown in Figs. 2 and 3 when used are spaced apart slightly from the line screen, and the opaque dots a and b and the intersecting points of the lines it should be on a line with the point 0 in Fig. 6, whereas the screens shown in Figs. 4 and 5 are used in contact with the line screen 10 so that the opaque elements 0 and d should exactly coincide with the intersection of the lines it. By the use of the term pitch I refer to the numbers of dots or points of intersection per inch, and it will be seen therefore that where the intersecting lines of the line screen are of a.

certain pitch, the opaque elements on the screens should be of slightly different pitch in one case, and should coincide in the other. Referring to Fig. 6, when a half-tone negative is to be produced according to my invention, the object is sharply focused in a camera on the focusing screen 6. 0 represents the optical center of the lens. The ordinary line screen 10 is now adjusted in position f which will give the modulation desired. The screen 11 with the dots a. or b, is now adjusted in the position g, between the focusing screen e and the line screen, so that the projection from the lens 0 brings the intersecting points of the lines it and the opaque elements a or b as the case may be, on a straight line, which condition can obviously be carried out with all the said elements of the screen at the same time, owing to the small difference in pitch of the two screens, only by adjusting the distance between the two screens. This adjustment can easily be effected, and its accuracy can be ascertained by inspecting the focusing screen e. When the screens are correctly adjusted, the lens is covered and the sensitive plate is substituted for the focusing screen 6, then the projection can be made as usual. When the exposure is made, the shades and the tones approaching the same will assume essentially the same character as those on the sensitive plate which is exposed in the ordinary manner through the line screen alone, the dot screen here having practically no effect. In the high lights, however, it is different. Here the lines on the dot screen will at a. certain exposure by developing the negative, fully disappear, but the dots a or b, which as shown in Figs. 2 and 3 respectively, may be of somewhat larger area than the intersecting points of the lines it on the screen 10, and which are also nearer to the sensitive plate, will protect parts of the plate against the light. It will be readily seen that a negative produced in this manner will in the shades have the aspect of an ordinary half-tone negative made by means of a common line screen, but in' the high lights it will look more like a negative taken through a screen of double the pitch of the line screen. In the transitional stage between the high lights and the medium tones, the intersections of the line screen will give rise to quite small dots on the negative, while the elements of the dot screen here cause the formation of somewhat larger dots. It will be understood, of course, that both screens remain in the camera during the whole exposure.

It will be seen that if the same lens or another is used, and its optical center after focusing assumes the position 0 (see Fig. 6), while the line screen 10 keeps the position 7, the correct relative osition of the lens and screens can be obtalned only by displacing the screen 11 to the point 9 thus bringing the dots a to the points (1 and it will be seen that the points of intersection of the same straight line as indicated in the diagram, and this action will take place with all the elements of the dot screen. It will be observed that it is necessary to have each element of the dot screen, its corresponding intersection of lines on the line screen and {he optical center of the lens, on a straight As shown in Figs. 4 and 5, the elements 0 and a) have such dimensions and shapes that they can be fully covered by the intersections on the line screen, and such screens can be used for obtaining a similar effect to that obtained in the above described manner. The line screen 10 and the screen 11 having the elements 0 and 11, must in this case have their opaqiie' elements on the surface of the sensitive plate which is not protected by a covering glass plate, so that the said surfaces can be brought into contact with each other, and with the'elements 0 and d exactly registering with the intersections in the line screen. It is obvious that this combination of contacting screens will have exactly the same effect as would the arrangement abovenoted.

A In Fig 7 112. represents a sensitive plate, k the dot screen, with elements 0 and d, and n the line screen, whereas 37 represents the lens. The sensitive plate is here given a relatively long exposure through the two screens, after which the exposure is interrupted and the screen it is removed, While the screen remains in its place, after which an additional exposure takes place during which the shades are not materially altered, while in the high lights only part of the spots which form the printing elements, are protected by the screen elements and d, and the result will be as in the former case, that there is a smaller number of printing elements in the high lights than if the line screen alone had been used.

It will be readily seen that where screens with the elements a and b, as shown in Figs. 2 and 3, are used the pitch of the screens must be a little more than double of that of the line screen, owing to the small distance between the screens during the exposure (see Fig. 6) while the dot screens with the elements 0 or d as in Figs. 4: and 5, must have said elements corresponding exactly to twice those of the said screen, as same must register exactly when in contact.

In carrying out my improved invention where the line screen and dot screen are spaced apart slightly as in the diagram, Fig. 6, and the whole exposure is made with the screens in this relation, the effect in the shadows will be about the same as if the line screen only were used, but in the high lights a much better effect is produced because the dots a or b protect the plate and also form supporting points for the paper lit Ill

lens 7:. and the elements a will be on the during printing; and furthermore because of the difierence in pitch between the intersecting lines on the-line screen and the dots of the dot screen, We get a greater distance of printing elements on the plate. I claim 1. The herein described method of producing half-tone negatives, which consists in making the exposure upon a sensitive plate simultaneously through screens of different characters and pitch,- and keeping the said screens in place during at least part of the exposure.

2. The herein described method of making half-tone negatives, which consists in making the exposure simultaneously through a line screen and a dot screen upon a sensitive plate for a certain period, then removing the line screen and completing the exposure through the dot screen only.

3. The herein described method of making half-tone negatives, which consists in arranging a line screen and dot screen in front of a sensitive plate, the opaque elements on the dot screen being less in number than the intersecting points of the lines of the said screen, and then making the ex; posure simultaneously through both the said screens upon the said sensitive plate.

4. The herein described method of making half-tone negatives, which consists in arranging a line screen and dot screen in contact and in front of a sensitive plate,

then making the exposure for a certain time through both the said screens, and compelling the exposure through the dot screen onl Iii testimony whereof I have affixed my signature in presence of two witnesses.

WERNER ROBERT BUSOH LARSEN. Witnesses:-

VIGGO BLoM, CEQIL VILHELM SoHoU. 

